Many people are consuming books in digital form through use of a wide variety of electronic devices. Among these electronic devices are electronic book reader devices, cellular telephones, personal digital assistants (PDAs), tablets, netbooks, and the like. As more electronic books (or “eBooks”) become available, more readers are opting to read books in digital form over the traditional paper-based form. Consumption of eBooks on electronic devices affords more opportunities to observe how readers interact with the content. One key opportunity is to better understand readers' knowledge of terms and to find ways to improve reader comprehension.